Means for preventing frosting of evaporator heat exchangers



. FIG. 3.

Shun/WM FREDERICK M. JONES JONES MEANS FOR PREVENTING FROSTING OF EVAPORATOR HEAT EXCHANGERS Flled Jan 2, 1943 FIG.

FIG. 2.

May 31, 1949.

Patented May 31, 1949 MEANS FOR PREVENTING FROSTING OF EVAPORATOR HEAT EXCHANGEBS Frederick M. Jones, Minneapolis, Minn., assignor, by mesne assignments, to U. S. Thenno Control 00., Minneapolis, Minn., a corporation of Minnesota Application January 2, 1943, Serial No. 471,206

My invention relates to means for preventing frosting of evaporator heat exchangers, and has for its object to provide, in combination with the '1 Claims. (Cl. 62-129) the temperature of the whole mixture of air will .be above the freezing point, will result in preventing the formation of frost on the heat exchanger In general practice in refrigerating compartments such as those of domestic refrigerators, and of commercial storage compartments including compartments for the transportation of perishables, the air is drawn from the compartment and passed through the evaporator heat exchanger and thereafter forced back into the compartment. This circulation of air normally carries all of the air moved from and back into the compartment. In practice the stream of air returning has been limited in volume so that even though when it enters the evaporator heat exchanger it is at a higher temperature than the surfaces of the coils, the contacting films of it are sufflciently cooled on said surfaces to deposit moisture and produce frost. I have discovered that the volume of air moved through the coils of the evaporator heat exchanger may be very greatly increased by driving a portion of the already cooled air directly back through the coils of the evaporator heat exchanger. In this way, many times, in practice five or six times, the volume of air which it is practical to send through the heat exchanger from the compartment can be caused to go through the evaporator heat exchanger. This is because too great a circulation of air in the compartment which is being cooled will have a correspondingly too great tendency to dehydrate the contents of the compartment. Only a limited flow, limited by the need of preventing dehydration of contents is practical to be moved into and from the compartment through th evaporator heat exchanger, but with the use of my invention any amount of air can be moved through'the coils, and a suflicient amount and at sumcient speed to continually wipe all the surfaces of the cooling coils with fresh volumes of air so that the formation of frost is prevented.

It is a principal object of my invention, therefore, to arrange a casing about an evaporator heat exchanger and the air-moving means therefor so 2 that a large part of the air drawn through the evaporator heat exchanger will be returned directly to the heat exchanger and only a relatively minor part of the air drawn through will circulate in the compartment.

It is a further object of my invention to provide a blower or fan having a capacity for moving air greatly'in excess of that required to circulate air in the compartment, together with means in the air passages such that a large part of, the air moved can be recirculated directly through the evaporator heat exchanger.

It is a further object of my invention to form about an evaporator heat exchanger a'casing having its walls spaced from said heat exchanger and provided with inlet and outlet passageways and forming a branch passageway leading from the outlet passageway tothe front of the evaporator heat exchanger, and provide a blower for moving air in said casing to cause the smaller part of said air moved to be drawn through the inlet passagewayand discharged through the outlet passageway and the larger part of the air moved to gothrough the branch passageway and be recircu lated through the evaporator heat exchanger.

It is a further object of my invention to provide a casing surrounding the heat exchanger and forming inlet and outlet passages therefor with damper means for varying the area of inlet'and outlet whereby more or less of the air moved by the blower may be caused to pass through the evaporator heat exchanger.

It is a further object of my invention toprovide hand-controlled means for regulating the aforesaid damper means.

It is a further object of my invention to provide means for causing a part of the air passing to the heat exchanger from the compartment and being recirculated through the heat exchanger to go over suitably wet surfaces so that the moisture content thereof will be increased and may be caused to approach saturation.

It is a further object of my invention to arrange the evaporator heat exchanger and blower in a cabinet closed excepting for the openings into the outlet and inlet passages to and from the outside and to arrange passages in said cabinet suitably proportioned and positioned for carrying out my invention.

The full objects and advantages of my invention will appear in connection with the detailed description thereof which will be given in the appended specification, and the novel features of my invention bywhich the aforesaid highly ad- 3 vantageous results are obtained will be particularly pointed out in the claims.

In the drawings illustrating an my invention in one form- Fig. 1 is a part sectional elevation view of an assemblage of devices for carrying out my invention.

Fig. 2 is a transverse sectional view taken on application of Fig. 5 is a fragmentary sectional view taken on line 55 of Fig. 3.

My invention is here shown as applied to a self-contained air-conditioning unit adapted to be put in awall ill of a compartment such, for example, as the compartment of a truck or of a meat storage compartment of a butcher shop, such as is shown and described in my application Serial Number 404,596 now Reissue Patent 23,000, dated May 11, 1948. A part of the casing H is adapted to be positioned outside of wall 50 as shown in Fig. 1. Part contains a compressor, a condenser, a motor to operate the compressor and means to move air through the condenser and for cooling the compressor, none of which is shown in detail for the reason that of themselves these instrumentalities form no part,

of my invention. It will be apparent also that the invention may be employed in connection with any type of means for getting compressed refrigerant to the evaporator coils of the evaporator regardless of how the same may be mounted. I Within the chamber to be cooled (not designated) and within the limiting confines of its walls I is a casing A having upper and lower walls l2 and I3, side walls I4 and I5, rear wall l6 and front wall All of these walls are plane surface rectangular walls except the front wall H, which is preferably curved inwardly, as indicated at l8, below a wide passageway l9 extending between the top wall I2 and a wall 20. This passageway l9, extends the full width of the casing between side walls l4 and I5. It is of horizontal construction and opens at its inner end into a second passageway 2| which is formed between top wall l2 and a transverse inner partition wall 22. Wall 22 curves downwardly at 23 to form a vertical partition 24 parallel with and spaced substantially from the rear wall l6. At a point 25 the wall 24 curves inwardly to form a second horizontal partition 26 extending between side walls l4 and I and secured to rear than has been customarily employed merely for circulating air in the chamber being cooled, since, as heretofore pointed out, too rapid circulation of air in such a chamber would result in too great dehydration of the contents subjected thereto.

In the practice of my invention, however, the

desired reater volume of air can be moved because only a minor part of it circulates in the chamber being cooled.

The front wall I1 is provided with an opening 35 through which air from the compartment being cooled may be drawn. eBranch passageway 2| opens through a passageway 36 extending across between side walls I5 and I6 into a chamber 31 formed in front of the evaporator heat exchanger 38. The back of the evaporator heat exchanger is spaced a distance, indicated at 33, from the opening 32 into the chamber of blower 33. On the bottom wall I3 is a mass 40 of wet material spaced. at 4| below evaporator heat exchanger 38. This space permits some of the circulated air to pass under the evaporator and over the wet surface of the material 4|) to pick up additional moisture so as to keep the air within the evaporator chamber and the chamber gree across branch passageway l9 or across passageway 36, according to whichever direction it is turned. An arm 45 on shaft 43 is connected by a link 41 to an arm 48 on a shaft 49 journaled on the front wall i! above opening 35. Upon shaft 49 is rigidly connected a damper 50, Fig. 1. Upon shaft 43 is a handle member 5|, Fig.

4,'and a ratchet wheel 52, the latter being engageable with a pawl 53.

The weight of damper 50 is sufficient to keep the ratchet teeth 54 in engagement with pawl 53.

In operation, when the parts are as shown in Fig. 1 and the blower 30 is in operation, the damper 45 will be-in a neutral position in line with the bottom wall'20 of air passageway l3 and air drawn into the blower will come simultaneously through opening 35 and from branch passageway 36 to the chamber 31 in front of the evaporator heat exchanger 38 for recirculation of the air that has gone through the evaporator heat exchanger and is being driven through pas-' sageway 2| by the blower.

In this position the cross-sectional area of the inlet to branch passageway 36 will be substantially double that of passageway l3, and flow of air through branch passageway 35 will be further. aided by the fact that there are both positive pressure behind the air in passageway 2| and negative pressure in front of the air in chamber 31. The result will be that something like three or four times as much air will be recirculated within the'evaporator chamber, and will be passed across the coils of evaporator 38 and under the evaporator through passageway 4| as will be circulated in the chamber to be cooled. This means that with a suflicient amount of air circulating in the chamber to be cooled three or four times that volume will be added to the air passing through the coils of the evaporator heat ex-' changer. This procedure causes the large volumei of air which is being recirculated to be cooled to a temperature which is substantially equal to that of the surface of the evaporator and thus minimize the formation of frost on the evaporator.

' since recirculation will cause the air to be in a evaporator.

some moisture on the coils orpick 'up moisture from the wet surface il it will be in a saturated saturated condition at the temperature of the While the incoming air may deposit condition before returning to the storage space to prevent dehydrating the products carried in the compartment. However, the large volume of recirculated air continuously flowing through the evaporator will perform a wiping action and will maintain imelf in a saturated condition at the temperature of the evaporator and thus substan- If, however, the reversels desired and the damper 6B is swung in the opposite direction it will narrow the entrance opening into branch passageway 36, and increase the width of opening 55, resulting in a greater relative amount of air circulated in the chamber to be cooled and less air recirculated in the evaporator chamber.

The primary and fundamental advantage of my invention resides in the fact that there. is a suficient volume of air passed over the cooling coils of the evaporator heat exchanger, most of it recirculated, to keep the surfaces of those coils in a condition such as to prevent the formation of frost. At the same time this makes possible a result of cooling the chamber witha minimum circulation of air therein.

A further advantage resides in the fact that due to recirculation within the evaporator chamber the air delivered to the chamber to be cooled will be at a more uniform and lower temperature than would otherwise be the case, and, therefore,

air from the room into the chamber, means for varying the area of the inlet opening, anoutlet passageway permitting air to be forced from the chamber into the room, means for varying the cross-sectional area of the outlet passageway, a

blower for causing air to move through the evaporator heat exchanger and to and through the outlet passageway, and a second passageway connected with and of greater cross-sectional area than the-outlet passagewayconnected with the part of the chamber in front of the heat exchanger for directing a larger part of the air moved by the blower to cause it to pass back to the front of the evaporator heat exchanger and to be recirculated therethrough and through the blower for greatly increasing the volume of air passing through the evaporator heat exchanger relative to the volume of air delivered to the room.

2. In combination with an evaporator heat exchanger, a casing in which it is positioned forming an enclosure having its front and rearends and top and bottom enclosing and spaced from said heat exchanger to form interconnected front, rear, top and bottom chambers, an air inlet opening to said front chamber, an air outlet-opening and passageway from said top chamber of much less cross-sectional area than that of the topchamber, the connection between the top chamber and the front chamber being of greater crosssectional area than that of the air outlet opening, and a blower in the rear chamber for drawing air through the evaporator heat exchanger from the front chamber and discharging it into the top chamber, whereby a large volume of the air moved by the blower and cooled in passing through the heat exchanger will go into the front chamber from which it will be recirculated through the heat exchanger.

3. In combination with an evaporator heat exchanger, a casing in which it is positioned forming an enclosure having its front and rear ends and top and bottom enclosing and spaced from said heat exchanger to form interconnected front, rear, top and bottom chambers, an air inlet opening to said front chamber, an air outlet opening and passageway from said top chamber of much less cross-sectional area than that of the topchamber, the connection between the top chamber and the front chamber being of greater crosssectional area than that of the air outlet opening, and a blower in the rear chamber for drawing air through the evaporator heat exchanger from recirculated through the heat exchanger.

- 4. In combination with an evaporator heat exchanger, a casing in which it is positioned forming an enclosure having its front and rear ends and top and bottom enclosing and spaced from said heat exchanger to form interconnected front,

rear, top and bottom chambers, an air inlet opening to said front chamber, an air outlet opening and passageway from said top chamber of much less cross-sectional area than that of the top chamber, the connection between-the top chamber and the front chamber being of greater crosssectional area than that of the air outlet opening, a blower in the rear chamber for drawing air through the evaporator heat exchanger from the front chamber and discharging it into the top chamber, whereby a large volume of the air moved by the blower and cooled in passing through the heat exchanger will go into the front chamber from which it will be recirculated through the heat exchanger, and an interconnected damper 'the inlet passageway, said casing having an outlet opening, another part of said chamber forming an outlet passageway from the rear of the evaporator to the outlet opening, said outlet passageway being divided into two portions, a first 'of said portions being of substantially greater cross-sectional area than the remaining portion, a branch passageway connecting the first portion of said outlet passageway and the inlet passageway, and a blower positioned behind the evaporator and operative to draw air from the inlet passageway through the evaporator and to dis- 6. combination with a refrigerant evaporator, a casing having its walls spaced from the evaporator 50 as to form a chamber surrounding the evaporator, part of said chamber in front of the evaporator being an inlet passageway to the evaporator, said casing having an opening into the inlet passageway, said casing having an outlet opening another part of said chamber forming an outlet passageway from the rear of the evaporator to the outlet opening, said outlet passageway being divided into two portions, a first of said portions being of substantially greater cross-sectional area than the remaining portion, a branch passageway connecting the first portion oi said outlet passageway and the inlet passageway, a blower positioned behind'the evaporator within said compartment and intermediate the front and rear surfaces of said compartment so as to be spaced therefrom, air moving means within said compartment between the'inlet and the outlet and on one side of said refrigerant evaporator, an intermediate passage forming communication between the discharge oi. said air moving means and the outlet, a branch passage forming communication between said intermediate passage and the side of said evaporator oppor 4 site the air moving means for recirculating a portion of the discharged air into contact with the evaporator, the cross-sectional area of said branch passage being substantially greater than the cross-sectional area of the outlet whereby a major portion of the discharged air is returned through the branch passage for recirculation in contact with the evaporator, and air flow control means carried in said intermediate passage having a first extreme position relative to the outlet to substantially completely terminate the flow of discharged air through the outlet, said air flow control means having a second extreme position relative to the branch passage for diminishing; the volume of the discharged air which is recirculated in contact with the evaporator whereby a residual portion of air is always recirculated into contact with the evaporator.

MDERICK M. JONES.

REFERENCE? @E'ZIIEED The following references are oi record in the file of this patent:

UNITED STATES PATMTEE Number Name Date 1,861,158 Hilger May 31, 1932 2,198,449 Alklns Apr. 23, 1949 2,236,190 Wolfert Mar. 25, 1941 

